How To Add Previous / Next Links to Blog Posts (CSS Help)

Hi Everyone,

I am looking to add previous and next buttons to my individual blog/journal posts.

An example of what I would like to add can be seen here (notice the prev and next buttons for the individual post and how by click them takes you to the previous or next post):

https://www.bluefuze.com/2010/11/29/portrait-of-my-daughter-work-in-progress/

My blog/journal can be seen here (different theme than link above): https://illiam.com/journal

And here is an individual post of mine from the blog/journal link above (this is where I would like to add the prev / next buttons for individual posts such as this one): https://illiam.com/graffiti

Currently I have done this:

In index.php, right before:
<?php include(TEMPLATEPATH."/sidebar.php");?>

I added this:

<div class="navigation">
<div class="alignleft" id="prevpostlink"><?php next_post_link('%link', '', TRUE); ?></div>
<div class="alignright" id="nextpostlink"><?php previous_post_link('%link', '', TRUE); ?></div>
</div>

In my style.css I added:
[CSS moderated as per the Forum Rules. Please just post a link to your site.]

However, after doing this, the next arrow (the light blue arrow on the right) is showing up on my https://illiam.com/journal page and not for individual posts.

I need help getting the arrow on the individual posts page and not on the main journal page. Thank you!